Automatic control of mobile craft



Jan. 24, 1961 P. A. NoxoN ET A1.

AUTOMATIC CONTROL CF MOBILE CRAFT Original Filed Oct. 25, `1946 6Sheets-Sheet 1 Jan.v 24, 1961 P. A. NoxoN ET AL 2,969,505

AUTOMATIC' CONTROL OF MOBILE CRAFT Original Filed Oct. 25, 1946 6Sheets-Sheet 2 Z Vviga 2 SECOND CROSSING OF BEAM FIRST CROSSING OF BEAMVOLTS TIME VOLTS TIME I I I I VO LTS TIME l lNvENToRs PAUL A. NOXON ALANM. MAC CALLUM ALFRED BENNETT TORNEY Jan. 24, 1961 P. A. NoxoN ETALAUTOMATIC CONTROL oF MOBILE CRAFT Original Filed Oct. 25, 1946 6Sheets-Sheet 3 INVENTORS PAUL A. NOXON ALAN M. MAC CALLUM ALFREDM.BENNETT ATT RNEY Jan. 24, 1961 P. A. NoxoN ET AL 2,969,505

AUTOMATIC CONTROL OF MOBILE CRAFT Original Filed Oct. 25, 1946 6Sheets-Sheet 4 lll-Z T u A Ei x W INVENTORS PAUL A. NOXON g 232 230 23341 l L l TIIIIIIIIE ALAN M. MAC cALLuM L ALFRED M. BENNETT ATTORNEY Jan.24, 1961 P. A. NoxoN. ET AL 2,969,505

AUTOMATIC CONTROL OF' MOBILE CRAFT OriginalFiled Oct. 25, 1946 6Sheets-Sheet 5 INVENTORS PAUL A.NoxoN a ALAN M. MAC cALLuM Z//I/gnALFRED M. BENNETT BY ATT RNEY Jan. 24, 1961 P. A. NoxoN ET AL 2,969,505

AUTOMATIC CONTROL. OF' MOBILE CRAFT Original Filed Oct., 2 5, 1946 I 6Sheets-Shee'# 6 INVENTORS PAUL A. NOXON ALAN M. MAC CALLUM 285/@ Z7 oALFRED NLBENNETT 284 283 v BVMI: :nl

ATTORNEY AUTOMATIC CONTROL F MOBILE CRAFT Paul A. Noxon, Tenatly, andAlan M. MacCallum, Maywood, NJ., and Alfred Bennett, New York, N. Y.,assignors to The Bendix Corporation, a corporation of Delaware Originalapplication Oct. 25, 1946, Ser. No. 705,52@

now Patent No. 2,592,173, dated Apr. 8, i952. Divided and thisapplication Dec. 23, 1950, Ser. No. 202,552 Y 13 Claims. (Cl. 328-427)The present invention relates to electric computing means for use inradio guidance systems for aircraft for controlling the latter inattitude and direction and constitutes a division of application SerialNo. 705,524, filed October 25, 1946, and now U.S. Patent No. 2,592,173issued April 8, 1952.

Radio guidance systems for aircraft usually employ at the radio receiveroutput a Cross pointer indicator which consists of a normally verticallocalizer pointer and a normally horizontal glide path pointer, wherecourse and -attitude errors appear, respectively, as D.C. voltagesacross the terminals of the two pointers. These voltages are utilized toorder the flight path of the craft in the horizontal plane as called forby the localizer signals and in the vertical plane as called for by theglide path signals.

Known control systems making use of such error Voltages have treatedthem as displacement functions plus the time derivatives thereof.Systems based on this concept, therefore, have certain inherentdisadvantages. First of all, the error signal derived from the radiosystem represents not a linear displacement from the desired ilight pathbut rather the angle subtended between the llight path and a line drawnfrom the craft to the transmitting station. Hence, unless range factoris employed, widely differing time constants will appear at differentranges giving rise to either low sensitivity at a relatively remotepoint from the runway or instability as a result of overcontrol at apoint relatively near the runway. Secondly, due to rellections fromterrestrial objects, the llight path set up by the radio equipment isnever a truly straight line but contains many bends of varying amplitudeand length. Derivative systems will, therefore, tend toward amplifyingsuch bends and create disturbances in the llight path of the craft outof all proportion to the actual amplitude of the bends themselves.Furthermore, if attempts are made to produce a more nearly rectilinearradio path by higher radio frequencies and more highly directionalsystems, there invariably appear regions not far from the flight pathhaving voltage gradients which drop instead of rise, causing derivativesystems to read the wrong algebraic sign and hence produce instabilityrather than damping.

The present invention overcomes the limitations of prior artarrangements by rejecting proportionality constants and recognizing onlythe algebraic sign of the error signals and, further, employing a timeintegral to order a heading or glide angle of the craft, the timeintegral of the error signal being accomplished in such a manner as toprovide damping.

An object of the present invention, therefore, is to provide a novelcontrol for an aircraft in automatic approach to a desired destinationfrom existing localizer and glide path radio systems.

Another object of the present invention is to provide a novel automaticapproach control system for aircraft for directing the craftautomatically toward and onto a aired States atent ICC desired runway,the system being responsive to the polarity of the incoming radio signaland the time of persistence thereof rather than the amplitude of theradio signal as heretofore.

A further object is to provide a novel apparatus comprising two units,'one of which will automatically control an aircraft along a visualrange beam, while both will act together to control the craft in twoplanes for automatic landing thereof.

Another object is to provide a novel flight path computer unit forautomatically controlling the rudder and ailerons of an aircraft tomaintain the flight of the latter along a desired radio beam.

A further object is to provide a novel glide path co1nputer unit forautomatically controlling the elevator and throttles of an aircraft forautomatically guiding it along a vertically inclined beam toward arunway.

Another object is to provide a novel automatic `approach system which inresponse to radio beams provides a constant magnitude signal which isintegrated with respect to time so that the longer an aircraft is awayfrom one or both of the beams the greater will be the control signaldeveloped for returning the craft to the beam.

A further object of the present invention is to provide an automaticapproach system for aircraft of the character described with a novelfeed-back arrangement whereby the craft is returned more rapidly to adesired beam.

The above and other objects and advantages of the invention will appearmore fully hereinafterfrom a consideration of the detailed descriptionwhich follows, taken together with the accompanying drawings wherein oneembodiment of the invention is illustrated. It is to be expresslyunderstood, however, that the drawings are for the purpose ofillustration and descriplion only, and are not designed as -a definitionof the limits of the invention.

In the drawings, wherein like reference characters refer to like partsthroughout the several views:

Figure 1 is a block diagram illustrating the various connections of thenovel automatic approach control system hereof with an aircraftautomatic pilot;

Figures 2 to 5, inclusive, are graphic illustrations representing craftflight path and the voltage outputs of the compass and integrationdevices as well as the voltage input into the automatic pilot channels;

Figure 6 is a wiring diagram of the novel flight path computer unit ofthe present invention;

Figure 7 is a wiring diagram of the novel glide path computer unit ofthe present invention;

Figure 8 is a wiring diagram of a relay arrangement determining theconnections between the flight path computer unit and the rudder andaileron channels; and,

Figure 9 is a wiring diagram of a relay arrangement determining thevarious connections between the glide path computer unit and theelevator and throttle control channels.

The novel automatic approach control system of the present invention isdesigned to operate with conventional localizer and glide pathtransmitters located at an airport to which the craft is heading. Thelocalizer transmitter is generally located at the far end of the runwayand radiates a radio pattern consisting of two overlapping lobes, one ofthe lobes being modulated at a frequency of cycles and so arranged as torepresent the left hand field of the localizer pattern and the other ofthe lobes being modulated at a frequency of cycles so arranged as torepresent the right hand eld of the localizer pattern. A line drawnthrough the center of the overlaps of each pair of lobes denes animaginary straight line down the center of the runway and out into spacefor some distance. The glide path transmitter, like the localizertransmitter, radiates a radio pattern consisting of two overlappinglobes modulated in a manner asaaos similar to the localizer except thatthe glide path lobes are stacked in a manner to provide verticalguidance of the craft, that is, a line drawn through the center of theoverlaps of each pair of the latter lobes will define an imaginarystraight and inclined line out into' space from the runway.

For guiding an aircraft to the landing field in accordance with both thelocalizer and glide path beams, conventional radio receivers, designatedgenerally with the reference characters liti and' il in Figure 1 of thedrawings, are mounted on the craft, the former receiving the verticalguidance signals from the glide path transmitter and the latterreceiving the lateral guidance signals from the localizer transmitter.inV a known manner, receiver il develops at its output a direct currentfiowing in one direction, assuming the craft to be to the' left of thelocalizer beam, and in an opposite direction when the craft is to theright of the localizer beam. Such directV current is communicated fromthe output of receiver ll by way of conductors 12 to energize a coil 13of a conventional cross pointer indicator M, a vertical pointer l5 beinginductively coupled with the coil to move in a clockwise direction froma normally central vertical position when the craft is to the left ofthe localizer beam and in a counter clockwise direction when the craftis to the right of the localizer beam it being understood that pointer)l5 maintains a normally centered vertical position when the craft isdirectly on the localizer beam at 'which time no current flows in coil13.

ln a similar manner, receiver l@ develops at its output a direct currentflowing in one direction, assuming the craft to be above the glide pathbeam, and in an opposite direction when the craft is below the glidepath beam. The direct current so developed is communicated from theoutput of receiver l@ by way of conductors lo to energize a second coili7 of indicator i4, a normally horizontal pointer i3 being inductivelycoupled with latter coil to move upward from its normally horizontalposition when the craft is below the glide path beam and downward whenthe craft is above the latter beam, it being understood that pointer lmaintains a normally centered horizontal position when the craft isdirectly on the glide path beam at which time no current flows ln coil17. So long as both pointers l5 and lb maintain their normally centeredposition as illustrated in Figure l, no current will be present ineither coil i3 or i7 and the pilot will be advised that the craft isheaded on the localizer beam and down the glide path beam.

As will now be understood,.the only information which the radio beamsactually present are the angles between the lines from the craft to thetransmitters and the axes of the beams, and not craft lateral distancesfrom the axes of the beams, regardless of the distance of the craft fromthe transmitters. l't is possible and it has been proposed, to control acraft using such angular information and its derivatives only, but asthe craft approaches the landing field, the sensitivity of the systemchanges, since the same angular error from the axis close to the landingfield represents a smaller actual distance from the beam than the sameangular error farther out from the field. Hence, it takes the craft lesstime to reach the beam from a given angular displacement close to thefield than it does when the craft is some distance from the field. lnorder to obtain proper control all along the flight path it is necessarywith displacement systems to continuously vary the ratio between thecontrol applied and the angular error calling for the control, inaccordance with the distance from the field. Moreover, the utilizationof straight displacement and. derivative systems implies a rapidresponse to the beams which may be dangerous when the beams are suddenlymaking the system hereof sensitive to the craft direction ofdisplacement, rather than the angle of displacement, and the length oftime that the craft is away from one or the other or both of the beamaxes. The signals developed in the system of the present invention foroperating the craft control surfaces are therefore not a function of theangle of craft displacement from the axes of the beams but depend uponthe. polarity of the radio signal or signals received during thedisplacement and upon the time of persistence thereof.

Referring now to Figure l of the drawings, the novel range and automaticapproach controls hereof are illustrated in a general manner, for abetter understanding of the present invention, in their connection withan all electric automatic pilot, which may be of the character describedand claimed in copending application Serial No. 516,488, tiled December31, 1943, and now US. Patent No. 2,625,348 issued January 13, 1953. Anautomatic pilot normally controls craft rudder, aileron and elevator'surfaces i9, 2d and 2l, respectively.

As more fully described in aforesaid application Serial No. 516,488,rudder i9 is automatically controlled in accordance with a heading orcompass signal developed by an earth inductor compassl 22, a rate signaldeveloped by a rate of turn gyroscope 23 and an electrical follow-backsignal developed by a follow-back device 24. As is known, compass 22develops a signal proportional to the amount of angular displacement ofthe craft from a prescribed heading which is fed by way of leads 25 tothe stator of an inductive device, located within a master directionindicator 2'6, which induces a signal in the rotor of the device that isfed to the input of a vacuum tube amplifier Z7 by way of leads 28, theamplifier output being connected by way of leads 29 to energize atwo-phase motor, within indicator 26, which operates not only to returnthe rotor of the inductive device to a null but also to move a pointeror scale relative to a fixed index to show the new heading as well as atransmitter device, located within indicator 2e, which, when actuated bythe motor, communicates by way of leads 3l?, a selector switchl andleads 32 to the input of a rudder channel amplifier 33, a signalproportional to the amount of craft departure from the prescribedcourse.

Fed into the input of the rudder channel of ampli- `fier 33, in serieswith the compass signal is a rate signal which is developed by rategyroscope 23 and its associated take-off, the latter being connected byway of leads 3d to the inputY of the rudder amplifier, the output ofwhich is fed by way of leads 35 to energize the variable phase of a twophase rudder servo motor 36, the fixed phase of which is energized by asuitable source of AC. current (not shown) by way of leads 37. Uponenergization, motor 36 displaces rudder i9 through a speed` reductiongear system 33 to return the craft to its prescribed course, the motoralso operating inductive follow-bacl device 2d which develops anelectrical follow-up signal communicated by leads 39 to the input of therudder amplifier to be there impressed in series with the displacementand rate signals for rudder control.

For craft attitude control, a gyro horizon it@ is pro- Ivided havingbank and pitch take-offs 41 and 42, re spectively, the former having. anelectrical signal developed therein in response to craft bank which isYfed by way of leads 43 to the input of an aileron channel amplifier 44,the output of the latter energizing the variable phase of a two phaseaileron servo motor 45 by way of leads 46, the fixed phase of which isenergized from a suitableV source of A C. current (not shown) by way ofleads d'7. Upon energization, the motor 45 displaces aileron 20 througha gear reduction system @i8 to re-establish level craft attitude andV atthe` same time operates an inductiVeVfollow-back deviceV 49 whichdevelops an electrical follow-up signal that isV communicated to theinput of the aileron amplifier by way of leads 50 to be there impressedon the bank signal for aileron control.

Pitch take-olf 42, onthe other hand, has an electrical signal developedtherein in response to a craft climb or dive which is fed by Way ofleads 51 to the input of an elevator channel amplier 52, the output ofthe latter energizing the variable phase of a two phase elevator servomotor 53 by way of leads 54, the fixed phase of which is energized froma suitable source of A.C. current (not shown) by way of leads 55. Uponenergization, motor 53 displaces elevator 21 through a gear reductionsystem 56 to re-establish level craft attitude and at the same time-operates an inductive followback device 57 which develops an electricalfollow-up signal that is communicated to the input of the elevatoratnplifier lby way of leads 53 to be there impressed on the pitch signalfor elevator control. The pilot system, generally described herein,therefore, is adapted for automatically controlling the various craftsurfaces in accordance with a predetermined course and attitude and,where an automatic turn control provision is required for the system,the turn controller unit of copending application Serial No. 665,918,filed April 29, 1946 and now U.S. Patent No. 2,618,446 issued November18, 1952. may be utilized. The pilot system, therefore, controls thecraft in azimuth and attitude in conformance with signals preselected bythe human pilot but for range flying or automatic approach and landingcontrol the pilot system is made responsive to radio beams emanatingfrom a ground station.

When the craft is to be taken in for a landing and is at that timedisplaced some distance from the localizer beam, for example, theproblem, mathematically, is one of determining the heading of the craftwhich will bring the craft on to the beam in the most gradual mannerconsistent with its distance from the beam and with a minimum ofoscillations relative to the beam once the beam has been crossed.

Should the craft be set simply to intersect the beam by following astraight line, as for example, by the line an infinit-ely long timewould be consumed before the craft could be made to follow the beam. Theangle at which the beam is intersected would (l) either have to besmall, resulting in a long period of travel before the craft wouldintersect the beam at an angle nearly parallel to the beam, or (2) alarge angle resulting in a quicker intersection of the beam (aperpendicular angle requiring the shortest distance to be traversed) butalso resulting in many intersections of the beam before the beam wouldbe tracked. The simplest way, obviously, is to correct the heading ofthe craft continuously as the craft approaches the beam. The problem isfurther cornplicated in that the craft does not respond instantaneousiyto control signals.

As the craft, Figure 2, is headed into the beam, the flight path isgradually changed until the beam is reached. As the craft intersects thebeam, it is travelling at an angle to the beam; consequently, it crossesthe beam. This means that a negative correction, Le., a correctionopposed to the initial correction for the craft, must be made. Thesequence is repeated from one beam intersection to another until theamplitude of the oscillations becomes negligible.

It is clear that the nearer the slope at which the flight pathintersects the beam at the new intersection is equal to the slope atwhich the path had previously intersected the beam, the longer theoscillation will continue. To damp the oscillations, therefore, theslope at which the ight path of the craft intersects the beam at a newintersection must be less than the slope at which it had previouslyintersected the beam. Obviously, also, in the system of Figure 2, eachhalf cycle represents different conditions, requiring a new set -ofconstants. Accordingly, only a single half cycle will be considered.

It may be assumed, for example, that craft 1, of Figure 2 is at somedistance x to the left of the beam there shown in broken lines and thatit is approaching the beam at a constant Velocity V, with its headingwith respect to the beam as the angle a, in which event the heading ofthe craft at any point x may be written as V sin a di (l) For smallvalues of the angle a the sine of the angle approaches the angle,permitting the Equation 1 to be written as da: Va (2) which representsthe change in heading.

Diiferentiating Equation 2 i (12x da The correction in heading or therate of change in.l

heading, i.e., the slope of line A, thus is assumed to follow a generalequation. This equation represents a group of exponential curves varyingfrom concave downward (when exponent b is greater than one), through astraight line (b equals one, to curves concave up wardly positive valuesof b less than one). The equation may then be written as d2x b dtz- VKt(4) By integration d:v -K Vt b+1) g- (b +1) +C (5) Since the equation isnow in terms of the slope of the line of ight A, the integrationconstant C is assumed to be the slope Vac, the first crossing of thebeam. This follows logically since the equation for the oscillation halfcycle from O to P is being considered and the line of flight intersectsthe datum with a slope Va, thus de KVuM E* @+B l-VOO (6) By a secondintegration,

K1/tbm Xrmivatfol 7) the integration constant C1 being Xo a point on thecurve that is the intersection of the flight path curve and the beam.Thus,

Substituting, for t in Equation 6 y@ '(b|1)(b|"2)o' Vvlofb-l- 2) -r Volo-Vaotwu From Equation 2 Vaga? +1) Letting the nominal slope value equala, and substituting in Equation 6 algebraically added to thedisplacement signal is satisfied by the voltages developed in novel timenetworks to be more fully described hereinafter. Empirically, it hasbeen found that where the exponent a substantially approximatesone-half, the most desirable results are obtained, the craft crossingand re-crossing the desired beam and then settling on the course in apath substantially as that indicated by curve A of Figure 2.

The time signals (localizer and glide path) referred to above, aredeveloped by novel night path and glide path computer'units generallydesignated with the reference characters 59 and 60, respectively, inFigure l. As generally shown in the latter figure, the input of the ightpath computer unit is connected by way of leads 61, switch 3i and leads62 with radio output leads l2 so that when switch 31 is turned to callfor localizer control the direct current energizing coil 13 of thecrosspointer indicator will likewise be communicated to the input ofunit 59, the output of the latter, including the compass signal which atthat time is fed through switch 31 to unit 59 by way of leads 63 (in amanner to be more fully described hereinafter), being fed into therudder and aileron'amplifier channels 33 and 44 by way of leads 64 and65, respectively.

The input of the glide path computer unit, on the other hand, isconnected by way of leads 66, switch 3ft and leads 67 with radio outputleads 16 so that when switch 3l is actuated to call for glide pathcontrol the direct current energizing coil 17 of the cross-pointerindicator will likewise be communicated to the input of unit 60. Theoutput of the latter is split so that a part of the signal is fed intothe input of elevator channel amplifier 52 by way of leads 68 forelevator control and another part of the signal is utilized for enginethrottle control. In the drawing of Figure l, the control is illustratedwith a twin-engined craft provided with throttle control levers 69 and70, each of which is provided with its own amplifier channel 71 and 72,each channel being generally similar to any of amplifier channels 33, 44and 52 which are shown in greater detail in the aforementioned copendingapplication Serial No. 516,488. A part of the output signal of unit 60is, therefore, fed into amplifier channels 71 and 72 by way of leads 73and 74, respectively, and the amplifier outputs are communicated by wayof leads 75 and 76 to the variable phases of two phase inductionthrottle servo motors 77 and 78, the fixed phases of which are connectedto a suitable source of A.C. current (not shown) by way of leads 79 and80. Upon energization, motor 77 displaces lever 69 to full throttle orretarded throttle position through a gear reduction system 31, the motoralso operating an inductive follow-back device S2. which develops anelectrical followup signal that is communicated to the input ofamplifier 71 in series with the signal of unit 60 by way of leadsl 83.Motor 78, on the other hand, when energized displaces lever 7d) to fullthrottle or retarded throttle position through a gear reduction system84, the motor also operating an inductive follow-back device whichdevelops a follow-up signal that is communicated to the input ofamplifier 72 in series with the signal of unit 60 by way of leads 86.

On automatic approach, therefore, the craft rudder is automaticallyactuated in accordance with heading, rate of change of heading,follow-up and ight path computer signals while aileron control isautomatically effected through heading, bank, follow-up and flight pathcomputer signals so that the craft is directed to the localizer beamalong a path substantially as that represented by curve A of Figure 2.Craft elevator, on the other hand, is automatically controlled inaccordance with pitch, follow-up and glide path computer signals whilethe throttles are automaticlly controlled in accordance with glide pathand follow-up signals whereby the craft is directed to the vertical orglide path beam for landing along a path also generally similar to thatrepresented by curve A of Figure 2.

Referring now to Figure 6 of the drawings for a more detaileddescription of the novel flight path computer unit of the presentinvention, designated generally with the character 59 in Figure l, whichdevelops the required time signal discussed above for directing thecraft on to the localizer beam along the path represented by curve A ofFigure 2, the unit as shown includes an electrical device 87 which isadapted for developing a reversible and workable A.C. signal from arelatively weak D.C. signal supplied thereto from radio receiver 11.

Device 87 comprises two permeable cores S8 and 89, each being providedwith center legs 90, 91 and spaced outer legs 92, 93 and 94, 95. Theouter legs are provided with primary energizing windings 96, 97, 9S and99 which are connected in series aiding relation with each other andwith a suitable source of A.C. current (not shown) and with secondarywindings 16d, 191, N2 and M3. Of the latter, windings Miti, liti areconnected in series opposed relation with windings 102, 103. Center legs90 and 91 are provided with a first pair of coils 104, 05 connected inseries opposed relation with a battery X06 and a pair of series aidingcontrol coils 197, w8 which are connected through leads 61 (Figure 1) tobe energized by the current owing in cross-pointer coil i3 when thecraft is to the left or right of the localizer beam. So long as nodirect current flows in control coils 167, MS the system is electricallybalanced and nothing appears at the secondary outputs. As soon, however,as the craft departs from the iiight path, a direct current fiows in thecontrol coils in one direction or another depending upon the directionof craft departure from the beam whereupon device S7 is unbalanced anddevelops at the secondary windings an A C. signal with reversing phaseand varying amplitude. For a-more detailed'description of the operationof device 874reference yis made Q to copending application Serial No.700,234, filed September 30, 1946.

The A.C. signal developed at the outpu-t of secondary windings 100, 101,102 and 103 is fed to a grid 109 of a vacuum tube 110 by way of a lead111 where it is amplified, the tube having a plate 112 connected by wayof leads 113, 114 with grids 115, 116 of a discriminator tube 117, lthelatter operating at its saturation point and having cathode 118, 119 andplates 120, 121. A.C. potential is applied to plates 120, 121 from aplate supply transformer 122 having a primary 123,

i energized from a suitable source of A.C. current, and

a secondary 124 which is connected at a center tap thereof with thecathodes by way of a lead 125 and at its outer ends with plates 120,121, respectively, by way of leads 126 and 127 and primary windings 128,129 of a pair of transformers 130 yand 131, the latter being the plateloads.

The sensitivity of the `system is such that tube 110 reaches saturationwhen the craft is off `the beam a very small amount and discriminatortube 117 is normally biased to cut-H so that with zero signal (when thecraft is on the beam) no voltage is present in secondaries 132, 133 oftransformers 130 and 131. When an A.C. voltage, however, is impressed ongrids 115 and 116 of tube 117, i.e., when the craft deviates from thebeam, the upper or lower portion of the tube becomes conductivedepending upon the polarity of the impressed signal, the polarity of thesignal, on the other hand, bein-g determined by the direction of craftdisplacement from the beam.

Assuming, for example, that the upper portion of tube 117 beco-mesconductive, an A.C. signal will be present at plate 120 which willappear at secondary 132 of transformer 130 and will be communicatedtherefrom by way of a lead 134 to a plate 135 of a dual rectifier tube136 having cathodes 137, 138 and a second plate 139, the latter beingconnected by way of a lead 140 with secondary 133 of transformer 131.

The output of the rectifier is connected by way of conductors 141 and142 wi-th the grids 143, 144 of a dual tube 145 having plates y146 and147 which are connected with the free ends of a split primary winding148 of a transformer 149, the winding being centrally tapped to a Bsupply by way of a lead 150. Tube 145 is provided with a normal negativecut-olf bias. Grids 143, 144 are connected to an A.C. grid supplycomprising a transformer 151 having a primary winding 152, energizedfrom a suitable source of A.C. current and a secondary winding 153connected to the grids through conductors 154 and 155.

interposed between the grids of tube 145 and the rectifier output is atime delay arrangement having a rapid time constant to the end that theautomatic approach system will not be oversensitive and apply control tothe craft in response to minute departures, the network from therectifier output thus constituting a rapid transient integrator. To thisend, an RC circuit is provided comprising resistors 156 and 157interposed between conductors 141 and 142 and condensers 158 and 159connected across the latter conductors, the resistors and condensersbeing grounded by way of a lead 160.

Referring now to the example assumed above, the direct current flowingin conductor 141, instead of being immediately impressed on grid 143 oftube 145, is delayed inasmuch as it must first change condenser 158 therate of charging being controlled by a resistor interposed in lead 141.This charge supplies the necessary bias for grid 143 whereupon tube 145becomes conductive and a signal appears at plate 146 and at winding 148.This signal persists in winding 148 until the charge on condenser 158leaks through resistor 156 to ground.

A mixing circuit including a secondary winding 161 and a resistor 162connected across its ends receives the signal from primary winding 148`and through an adjustable contact 163 communicates the signal by way ofa lead 164 to the grids 165 and 166 of a dual amplifier tube 167, plate168 of the tube feeding a signal into the rudder channel amplifier 33 byway ofV a transformer -169 whose secondary is provided with suitableconnections, to be hereinafter described, to leads 64 for connectionwith the rudder amplifier and plate 171 of the tube feeding la signalinto the aileron channel amplifier 44 by way of a transformer 172 whosesecondary is provided with suitable connections, to be hereinafter morefully described, to the leads 65 for connection with the `aileronamplifier. The arrangement thus far described takes care of any rapidtransients, say, for example, on the order of 0.5 second, and Ithe samesignal from computer 59 that c-ontrols rudder 19 also controls aileronsurfaces 20 to thereby provide coordinated turn of the craft to returnit on to the beam. At the same time a signal from compass 22 is also fedto the mixing circuit to be added algebraically with the signal of tubeby way of leads 63.

For transients that persist over a longer period of time, additionaltime `delay devices in the nature of thermal delay relays or tubes 173and 174 are provided having differing time constants. For example,device 173 may have a time constant of thirty (30) seconds while device174 may have a time constant of four (4) minutes. For a more detaileddescription of the nature land operation of such thermal delay devicesreference is made to copending application Serial No. 562,826, filedNovember l0, 1944, now U.S. Patent No. 2,463,805, issued March 8, 1949.

In the event that craft displacement from the beam represents adist-ance in time exceeding .5 second, a signal is picked up from eitherplate 135 or 139 of tube 136 by way of conductors 175, which are tappedto leads 134 and 140, and fed to the grid 176 or 177 of a seconddiscriminator tube, shown in Figure 6 as two separate tubes 178 and 179,whose action is similar to that of tube 117 in that either tube 178 or179 becomes conductive depending upon the polarity `of the signalimpressed on grids 176 and 177 by conductors 175.

Thermal delay device 173 comprises a sealed tube having mounted thereina pair of resistors 180 and 181 constituting two arms of a Wheatstonebridge, the remaining arms being outside of the tube and comprising asplitresistor 182 which is variably tapped by a conductor 183, thelatter connecting through a resistor 184 with a ground conductor 185which is connected to the junction of arms 180 and 181, conductors 183and 185 defining the output of the bridge when the latter is unbalanced.Bridge energization is obtained from a suitable A.C. source by way of atransformer having a primary 186 and two secondaries 187, 188secondary187 being connected to an opposite diagonal of the bridge by way ofleads 189. A resistor 190 is arranged in heat exchange relation withbridge resistor 180 and is connected in series with a plate 191 of tube178 by way of a lead 192 and with a second resistor 193 by way of a lead194, the free end of resistor 193 being connected by way of a lead 195with a screen grid 196 of tube 178.

Following the example through, which has been assumed above, in responseto a craft departure from the beam exceeding .5 second, an A.C. signalflows at plate 191 of tube 178 and is fed to resistor 190 which after agiven period of time (30 seconds) heats up to change the value of bridgeresistor 180 to unbalance the bridge and provide current flow in onedirection at adjustable contact 197 which is fed to a grid 198 of a dualamplifier tube 199, the signal appearing` at a plate 200 of the tubewhich is connected with a transformer whose secondary 201 is connectedin series with the compass signal fed into terminals 202 by way ofsuitable connections, to be hereinafter described, and with the mixingcircuit by way of a lead 203 so that the signal of device 173 aids thesignal of tube 145 and both are added algebraically with the 1 1 compasssignal for controlling rudder andaileroncraft surfaces.

If,.on the other hand, craft displacement from the beam exceeds indistance a time of four (4) minutes, second resistor 193 will heat upand because of its'heat exchange relation with a resistor 204 change thevalue of the latter. Resistor 2134 constitutes one arm of a bridgecircuit and it together with an adjoining resistor S, defining thesecond arm of the bridge, is located within device 174, the remainingtwo arms of the bridge being constituted by a resistor 266 which iscentrally tapped by a conductor 207, the latter being connected througha resistor 268 with a grounded lead 209 connected to the juncture ofarms 204 and 205, conductors 267 and 269 defining the bridge output.Bridge energization is obtained from secondary 188 which is connectedacross an opposite diagonal of the bridge by way of leads 211i.

The signal resulting from the unbalance of the bridge of device 174 iscommunicated by way of an adjustable contact 211 to a grid 212 of tube199 whereby a signal is developed at a plate 213 of the tube andcommunicated therefrom through the secondary windings 214 of atransformer 215 to be impressed in series with the signal of device 173.

In the event that the polarity of the signal fed by leads 175 to thegrids 176 and 177 is changed so that tube 179 becomes conductive ratherthan tube 178, an A.C. signal will appear at plate 216 of tube 179 andwill be cornmunicated by lead 217 to a third resistor 218 arranged indevice 173 in heat exchange relation with bridge arm 181 so that after aperiod of thirty seconds the value of resistor 181 will change tounbalance the bridge and provide reverse current flow at contact 197.Resistor 218 is connected in series with a further resistor 219 arrangedin device 174 in heat exchange relation with bridge arm 205 so thatafter a period of four (4) minutes, assuming, of course, the signal tobe present at plate 216, the bridge is unbalanced and reverse currentfiow occurs at contact 211. Resistor 219 is connected by way of a lead220 with a screen grid 221 of tube 179.

Where the circuit including the output of rectifier 136 and tube 145 hasbeen termed as a rapid transient integrator, the circuit includingthermal delay devices 173 and 174 may be termed a slow transientintegrator.

If, for some reason, the craft 1 of Figure 2 is away from the beam axis(which may be considered to be the localizer beam) and flight pathcomputer 59 isV in circuit with the automatic pilot, radio 11 willdevelop a direct current of a given direction in coil 13 which is alsocommunicated to control coils 107 and 108 of device 87 of the computer.coils, an AC. signal appears at the output of secondaries 180, 191,1G2and 103 and at grid 109 ofv tube 110 which is then amplified and fedto discriminator tube 117. Depending upon the direction of current iiowin control coils 167 and 1%, either the upper or lower portion of tube117 becomes conductive and since it operates at its saturation point, aconstant magnitude signal is applied to the integrating devices. As thetime of the constant magnitude signal increases, a control signal isfirst developed at the output of tube 145, a second control signal issubsequently developed by thermal delay device 173 to act with the firstsignal and, finally, a third signal is developed by thermal delay device174 which is added with the first two signals. The three integrationdevices, therefore, produce a resultant voltage that is the timeintegral of the constant magnitude signal at the output of discriminatortube 117.

lf the craft has been some distance from the beam but fiying` a courseAparallel with the beam no rudder control is effected by the compass, thelatter beingsatisfied. However, as soon as fiight path computer unit 59is electrically connected with the automatic pilot, the resultantvoltage developed by the integration devices actuates the rudder andaileron siirtaces to turn the craft in a direction As a result of D.C.flow in the control r aderisce thatn will bring it to thebeam axis, therate of turn being dependent upon the magnitude of the voltage developedby the integration devices, the magnitude of the voltage, in turn, beingdependent upon the time that the craft has been away from the beamV axisafter the flight computer has beenconnected with the automatic pilot.

I As soon as the craft turns toward the beam, compass 22 develops asignal which is opposite to the resultant voltage of the integrationdevices and the two operate in unison on the rudder and ailerons so thatthe degree of turn of the craft from its original heading is madeproportional to the Voltage from the integration devices. As timepasses, the voltage from the latter devices builds up from Zero, asshown graphically by curve B of Figure 4, and becomes larger and largeras the fixed input signal from discriminator 117 is integrated and thecraft change in heading toward the beam fro-m the original coursebecomes larger and larger. By the same token, asv the craft turns towardthe beam the sfgnal of compass 22 builds up from zero, in an oppositedirection, as shown graphically by curve C of Figure 3 of the drawings.The compass signal of Figure 3 and the signal `of the integrationdevices when added algebraically, provide an input signal into therudder and aileron channels of the automatic pilot of a character suchlas that represented graphically by curve D of Figure 5, this lattersignal determining the rate of turn ordered.

Sincel the craft is fiying at a definite speed and is turnirigtoward theaxis of the beam, it will eventually intersect the beam at a point y(Figure 2) at which time the voltage of the integration devices will beat a maxi mum as shown in Figure 4 and the compass signal also will beat its maximum Value as shown in Figure 3. At some point after the firstcrossing of the beam these voltages are equal and opposite so thatrudder will be centered. The instant the beam is reached, the D.C.signal in coil 13 of the cross pointer drops to Zero as does the signalin control coils 107 and 103 of device 87 whereupon the signal of theintegration devices starts to decay and drop toward zero as shown inFigure 4. While the signal of tube will dro-p to zero almost instantly,the signals o-f devices 173 and 174 will persist for a time because ofthe lag resulting from the `cooling of resistors 190 and 193.

As the craft crosses the beam, however, a reversed direct current flowsin'coil 13 ofthe cross pointer indicator as well as in the control coilsof device 37 whereupon the lower portion of discriminator tube 117becomes conductive and a signal appears, after a delay resuiting fromthe RC circuit, at plate 147 which is out of phase with the signaloriginally appearing at plate 146 of tube 145. The signal appearing atplate 147 is fed through tube 167 to the rudder and aileron channels fordisplacing the'rud-der and aileron surfaces in an opposite direction toturn the craft to the beam. At this point, the compass signal begins todrop toward zero as shown by curve Cof Figure 3 while the decay of thesignals of thermal devices 173 and 174 is speeded up by thesignal'appearing at plate 216 of tube 179.

Again, depending upon the length of time that the craft is displacedfrom the beam prior to its second crossing of the beam, a signal will befed by way of conductors 175 to grid 177 of tube 179 and a signal willappear at plate 216y thereof which will be fed to resistor 218 to heatthe latter and thereby unbalance the bridge of device 173 and, after afurther lapse of time, assuming the second crossing not yet t-o havebeen made, resistor 219 will heat up to unbalance the bridge of device174. While both bridges, in the latter case, wiil have a reversedcurrent flow at their outputs to add with the output of tube 145, thefull output of the bridges will not be available until the arms i andiii-4 thereof have cooled off entirely, that is, the signal appearing inboth bridges dueto the first'unoalance has disappeared. Beforethispoint'isreached, however, the decaying sig- 13 nals and the newsignals will be equal and oppositeso that their algebraic output will bezero. This condition is illustrated in Figure 4 where curve B crossesthe dashed line for the first time.

The new signals due to tube 145 and thermal devices 173 and 174 willfinally prevail and build up to reverse rudder and aileron surfaces andcause the craft to turn toward and cross the beam the second time in themanner shown by curve A of Figure 2. lf, after the second crossing, thecraft again goes beyond the beam, the reverse operation of the variousintegration devices occurs as discussed above until the craft hasassumed a ground track defined by the beam.

The integration of the constant magnitude signal of tube 117 is madenon-linear in order that the motion developed by the craft may bedamped. While a number of damped solutions exist, the one here chosenhas the criterion that at each intersection of the craft with the beamaxis the angle of intersection with the axis will be substantiallyone-half the angle of the preceding intersection. This leads to a motionwhich is a damped oscillatory wave of continuously increasing frequency.As the frequency of oscillation is increased, damping by the naturaldamping of the craft, and by rate device 23 increases, and the motioneventually becomes critically damped and oscillation ceases. In deadsmooth air oscillation may cease after the first overshoot.

Flight path computer 59, hereinabove described, may be used for eitherautomatically iiying range or the localizer path while glide pathcomputer unit 60 is adapted for flying glide path alone to bring thecraft on to the runway. Except for the fact that no compass signal isrequired for fiying, glide path computer unit 60 is substantially thesame as computer 59 in structure and operation.

As shown in greater detail in Figure 7 of the drawings, computer 60includes a device 230, similar to device 87 of Figure 6, for providing aworkable and properly phased A.C. signal at an output lead 231 thereofin response to a direct current flow in control coils 232 and 233thereof, the latter being connected by way of leads 66 and 67 (Figure l)with coil 17 of the cross pointer indicator 14. Thus direct current willflow in control coils 232 and 233 in one direction when the craft isabove the glide path beam and in a reverse direction when the craft isbelow the beam. Output lead 231 connects with grid 234 of a vacuum tube235 where the signal is amplified, the plate 236 of the tube connectingwith the grids 237 and 238 of a discriminator tube 239 and, dependingupon the direction of D C. fiow in the control coils, either the uppero-r lower portion of tube 239 becomes conductive to pass a signalthrough a rectifier tube 240, the output of the latter being fed togrids 241 and 242 of a dual tube 243 through a time delay circuit, ofthe character described in connection with unit 59, having a timeconstant of about .5 second.

The signal appearing at one or the other of the plates of tube 243 iscommunicated through the secondary winding 244 of a transformer 245 tothe grids 246 and 247 of an amplifier tube 248, the plates of whichprovide a signal through transformers 249 and 250 to the elevator andthrottle amplifier channels 52, 71 and 72 through connections to be morefully described hereinafter.

Aussming only a. slight deviation from the glide path beam,representing, for example, 0.5 second in distance from the beam, asignal will appear, properly phased, at either the upper or lowerportion of tube 243 for controlling elevator surface 21 and throttlelevers 69 and 70 to open or retarded position to return the craft to thebeam.

Where the craft is away from the glide path beam for a time equal to orexceeding thirty (30) seconds, a part of the output signal is fed by wayof leads 251 to either grid 252 or 253 of discriminator tubes 254 and255 to unbalance the bridge of a first thermal delay device 256 14whereby `an A.C. current flows at its output and is fed through theupper portion of a tube 257, a transformer 258 and a lead 259 to beimpressed in series with the signal of tube 243 for aiding in theoperation of the elevator and throttles.

If, on the other hand, the craft is away from the glide path beam for atime equal to or exceeding four (4) minutes, the signal at either tube252 or 253 will unbalance the bridge of a second thermal delay device260 4whereby an A.C. current will be caused to flow at its output and isfed through the lower portion of tube 257, a transformer 261 and lead259 to be impressed in series with the first two signals fed into theinput of tube 248 for elevator and throttle control. Thus, the furthercraft is from the glide path beam, either above or below it, the greaterthe resultant signal will be for controlling the elevator and throttlesto direct the craft to the glide beam. Generally considered, the outputof the three integration devices of the glide path computer take theform of curve B of Figure 4 in that the signal builds up from zero andattains its maximum value at the time that the craft returns to andcrosses the beam for the first time. Thereafter, the signal begins todecay while a reverse signal is developed which finally becomes equaland opposite to the decaying signal and thereafter builds up in thelopposite direction to reverse elevator and throttle control to directthe craft toward the beam along a path substantially as that representedby curve A of Figure 2.

While the compass signal utilized in connection with the flight pathcomputer unit is not required in connection with the glide path computerunit, the latter on developing a control signal which actuates theelevator is opposed by a signal developed by the pitch take-off 42 ofthe artificial horizon, the latter taking the form of curve C of Figure3 during the various headings of the craft, so that under certainconditions when the craft is returning to the beam the glide path signaland the pitch takeoff signal will be equal and opposite at which timethe elevator will be centered. This action is similar to that consideredabove in connection with the compass signals andthe signals of theflight path computer.

In the event that a failure occurs in some part of the computer network,tube 167 of unit 59, for example, would be passing too high a signalinto the rudder and aileron channels of the automatic pilot which isundesirable. Io the end that this condition, if it occurs, may beprevented, a safety device is provided in the nature of a doubleamplifier tube 265 (Figure 6), having a first grid 266 coupled with thegrids and 166 of tube 167 by way of a lead 267, the related plate 268,in turn, being connected with a grid 269 whose related plate 270` is incircuit by way of leads 271 with a solenoid coil 272 (Figure 8).

Normal current flow at plate 270 of tube 265 enerzies coil 272 to closea relay armature 273 with a fixed contact 274, the two being connectedby way of leads 275 with a solenoid coil 276 whereby the latter is alsoenergized to normally maintain relay armatures 277, 278 and 279 out ofengagement with related contacts 280, 281 and 282. The foregoing resultwill be achieved when a grounded sequence switch 283, carrying a contactsegment 284, has been set on power terminal 285.

Assuming switch 283 to have been moved to a localizer terminal 286,additional solenoid coils 287, 288 and 289 will have been energized tolift their related armatures 290, 291, 292, and 293, 294, 295 togetherwith 296, 297, 298, 299 from one set of fixed contacts 300, 301, 302,303, 304, 305, 306, 307, 308, and 309 to a lsecond set of fixed contacts310, 311, 312, 313, 314, 315, 316, 317, 318 and 319. In this manner thesignal of compass 22 is fed into computer unit 59 by way of leads 63(Figure l) which connect with terminals 320 and 321 of Figure 8. Theseterminls connect with terminals 202 of Figure 6 by way of leads 322through leads 323, 324,` armature relays 297, 299 and contacts 317, 319.By virtue of this provision,

15 the' compass signal instead of being fed directly to the rudderchannel 33 by way of leads 32 is fed into the computer unit, when thelatter is engaged with the automatic pilot, by way of leads 63 to bemixed with the signals of the integration devices for rudder and aileroncontrol. V

Under the foregoing condition, the signal from the cornputer 59 forrudder control is i'ed to terminals 325 and 326, connected through leads64 with the rudder channel amplifier, by way of leads 327, a fixedcontact 328 which is engaged by an armature 329, lead 330, tixedcontacts 311, 312, armatures 291, 292 and leads 331` and 332 While thesignal from the same computer for aileron control is fed to terminals333 and 334, connected through leads 65 with the aileron channelamplifier, by way of leads 335, a fixed contact 336, which is engaged byan armature 337, lead 338, iixed contacts 313, 314, armatures 293, 294and leads 339 and 341).

The direct current signal communicated to control coils 107, 108 ofdevice 87 of the computer from cross pointer coil 13 is conducted by wayof leads 62 to terminals 341 and 342, the latter connecting with leads61 (Figure 6) by way of a lead 343, armature 298, fixed contact 31S andlead 344, armature 290 and xed contact 31,0.

In the event that a failure does occur in the computer network, thevoltage on grid 269 of tube 265 (Figure 6) increases so thatsubstantially no current is available at plate 273 whereupon solenoidcoil 272 is de-energized and armature 273 disengages contact 274 and,simultaneously, solenoid coil 276 is de-energized to close its armatures277, 278 and 279 with contacts 280, 281 and 282. In this manner, theclosing of armature 273 and contact 281 places a short across leads 327and 33t), carrying the rudder signal from the computer unit, by way ofleads 345 so that the computer signal cannot pass to the rudder channelampliiier while the closing of armature 277 and contact 28@ places ashort across leads 335 and 338, carrying the aileron signal from thecomputer, by way of leads 346 so that the computer signal cannot pass tothe aileron channel amplilier.

At the same time, closure of armature 279 with contact 232 closes acircuit to a warning lamp 347, the latter being connected with agrounded terminal 348 by way of a lead 349 and with armature 279 by wayof a lead 350, contact 282, on the other hand, connecting through a lead351 and terminal 352 with a battery 353. ln this manner, in the case ofa failure in the computer network, warning lamp 347 glows to indicatethe failure visually while the computer output is prevented fromcommunicating, at that time, with the rudder and aileron controlchannels.

ln order to l'ly a glide path beam as well as the localizer beam, switch233 is turned to engage glide path terminal 354 (Figure 9) which placessolenoid coils 355, 356 and 357 across the power supply by way ofconductor 353 whereby the latter are energized to engage armatures 359,369 and 361 Awith fixed contacts 362, 363 and 364, the armatures havingnormally engaged contacts 36S, 366 and 367 and armatures 36S, 369 and37@ with fixed contacts 371, 372 and 373, these armatures havingnormally engaged contacts 374, 375 and 376 as well as armatures 377,378, 379 and 33th with xed contacts 381, 382, 383 and 334, the latterarmatures normally engaging contacts 335, 336, 387 and 383.

in a manner similar to computer unit 59, computer 6d is also providedwith a safety device in the form of a tube 389 (Figure 7) whose grid 390is coupled by way of a lead 391 with grids 246 and 247 of tube 243. Withswitch 233 on power terminal 235, normal plate current is available atplate 392 which is connected by leads 393 with a solenoid coil 394 forenergizing the latter whereby `an armature 395 is brought into normalengagement with aV x'ed Contact 396, the latter both being connectedthrough leads'"397 to energize a further solenoid coil 398 of leads'417,418, armatures 379, 359 and' contacts 383,-

Which, i` 1 1 turn, lifts` ,aimat ures 399, 40G and `401 from their xdcontacts 402,143' 1404 Urid'er normal operating conditions,therefo'r'eythejopt'- put of theglide path computer unitis fetdwthroughtransformer 249oftFigu`rew7 to terminals 405 and 406 of Figure 9, whichVconnect by` way of' leads 68 (Figure l) with the elevator channelamplifier, by way of lead s 4 (}7, oiitaiets 371, 372, armatures.; ses,369 andiesds 40s and 409 while the, computerpignaljorthrottle control isfed through transformer 250 of Figure 7 to terminals 410 and 411 ofFigure?, whichnconnect by way of leads 73, 74 (Figure 1)' with thethrottleAampliiier's, byyvayof leads 41,2, contacts 363, 364, armatures360, 361 and ieads 413 and 414;

Ther signal'wener'gizing coil fed by way of leads 67 (Figur e 1) toterminals 415 and 416 of Figure'9, the latter connectingwith leads 6 6,conf,l

nected to control coilsf232` and 2.33ct Figure 7, b y way v inthe eventthatnaV failureoccurs in the networh of1 computer unit 60, the gridsoftube 389 w` ill be driven flow at its plae 392 whereuponsolenoid coil394will bei de-ee'rg'iz'ed to open armature 395 withcontact 39,6.I As

a result solenoid coil393 will likewise de-energize closing' armatures'399, 464D with1contacts4tl2, 463 thereby placing a short across leads407by way ofv leads 4 1 9, preventgthe computer signal vfrom passing toterminals' 405, 4ti6'leading to the elevator channel amplilierand asecond short acrosjsfleads 412 `by way of leads 421, 422 to prevent thecomputer signal'from `passing to terminals 410,411 leading to thethrottle amplifiers. Siniult'ane-y ously, the closing of armature401with contact 404 causes a warning lamp 4 2 3 to glow indicating visuallythat a` failure has occurred the'ne'twork, one side of the lampconnecting with a grounded terminal 424 by` way of a lead 425v and theother side thereof connecting with a battery 426 through a terminal 427,lead 428, contact 405,4, armature 401 and a lead 429,

The flightl computer unit, above described,V is Vadapted for rangedyingY as well as for' ilying the localizer path. inasmuch as the crafttravels at a higher speed during range yn'g it is desirable to utilizeonly `a portionof the computer unit for rudder and aileron control. Tothis end Va selector switch 430' (Figure 8) is provided which for rangeflying is turned to range terminal 431', the latter connectingthrou'gh'a lead 432 with a lQnhnod coil 433, the free end of which isconnected by way of a lead 434'witha solenoid coil 435, the latterconnecting through a lead 436 with a suitable source o f power'.solenoid coilsl 433 and 43'5 are energized, they move armatures. 329and'337 linto engagement with iixedfconta'cts 437 and 433 which connectwithlead's 439 and440 (Figure 6) for conveying only av portion'ofthe'conputer signals to rudder and aileron terminals 325, 326 and ssa,334;

Inasniuch as the resultant signal of the integration device's'of both`computer units will not start to decay until the localizer and glidepath beams have been crossed, the time ofY decay may cover some periodto direct thecraft undesirably beyond either one or both of the beams.'The decay period, as will now be understood, will notstart until thesignalsk in coils 13 and 17 of tlre'cross pointer have dropped to zeroindicating that the craft at that instant is crossing both beams. To theend that the decay of thesignal of the integration devices may bespeeded up to'prevent the craft fromH goingbeg yond either or both ofthe beams an undesirable distance after a` crossing, alnovelanticipatory control is`fu'rther provided in the nature of a` doubleamplifier comprising tubesj441' and442 (Figure') and tubes 443 and 444(Figure'). The setub'es: are sobiased that a portionof the computersignalsisfedinto their grids 445 and 446.

17 of vthe vcross pointer is by way of leads 267 and 391, the platecircuits of tubes 441 and 443 supplying, through transformers 447, 448and leads 449 and 450, signals to the secondary windings of devices 87and 230 which are 180 out of phase with the signals in those windingsdeveloped by the direct current in the coils of the cross pointer. Byvirtue of this provision, a point will be reached before the firstcrossing of the beams where signals due to the radio signals are stillavailable at the secondaries of devices 87 and 230 but the signals oftubes 441 and 443 will become equal to these signals and since the feedback signals are of opposite phase the resultant signals at thesecondaries and tubes 110 and 235 will be zero so that the resultantsignal of the integration devices will start to decay even though thebeams have not yet been crossed. In a sense, therefore, due to the feedback devices just described arbitrary beams are set up to speed up craftarrival on to the desired radio beams.

In ying an aircraft equipped with the above-described novel apparatusfrom one airport to another, the human pilot may first ily on visualrange between the stations and then make an automatic approach on thelocalizer and glide path beams. After the take-off, the radio is tunedto the frequency of the visual range and the craft is flown to intersector bracket the beam, this condition being evidenced when verticalpointer 15 of the cross pointer indicator is at zero. Thereafter,sequence switch 283 is moved to power terminal 285 (Figure 8) for awarm-up interval and selector switch 430 is moved to range terminal 431.When the craft is in the desired position with respect to the beam,sequence switch 283 is moved to localizer terminal 286 and the craftwill be automatically own down the visual range system to itsdestination. As the craft approaches its destination and it is desiredto go into the automatic approach procedure, sequence switch 283 isturned back to power terminal 285 to disengage localizer control,leaving the craft under the control of the automatic pilot. Selectorswitch 430 is thereafter turned away from range terminal 431 and theradios are tuned to the frequencies of the approach system. The speed ofthe craft is then reduced to approach speed and the localizer beam isbracketed at which time sequence switch 283 is turned to localizerterminal 286. Thereafter the craft is own to intersect the glide beamand when the latter is intersected switch 283 is moved to glide pathterminal 354. The craft is then landed automatically.

As will now be apparent to those skilled in the art, a novel anddesirable apparatus has been provided for automatically guiding anaircraft in two planes and landing it at its destination, the systembeing of such character as to utilize the lamount of displacement of thecraft from either or both of the beams rather than the angle of suchdisplacement and the time that such displacement from the beam persists.

Although but one embodiment of the invention has been illustrated anddescribed in detail, various changes and modifications inthe form andrelative arrangement of parts, which will now appear to those skilled inthe art, may be made without departing from the scope of the invention.Reference is therefore to be had to the appended claims for a definitionof the limits of the invention.

What is claimed is:

l. An electrical computer unit comprising means responsive to a directcurrent for developing an alternating current signal Whose phase andamplitude are dependent upon the polarity and magnitude of said directcurrent, means connected with said last-named means for developing aconstant magnitude potential from said alternating current signal, andintegrating means responsive to said constant magnitude potential fordeveloping an alternating current potential whose amplitude varies as afunction of the time of persistence of said direct current.

2. An electrical computer unit comprising means responsive to a directcurrent for developing an alternating current signal whose phase andamplitude are dependent upon the polarity and magnitude of said directcurrent, means connected with said last-named means for developing aconstant magnitude potential from said alternating current signal, andan electrical integrationinetwork responsive to said constant magnitudepotential for developing an alternating current potential whoseamplitude varies as a function of the time of persistence of said directcurrent.

3. An electrical computer unit comprising means responsive to a directcurrent for`developing an alternating current signal whose phase andamplitude are dependent upon the polarity and magnitude of said directcurrent, means connected with said last-named means for developing aconstant magnitude potential from said alternating current signal, andintegrating means comprising at least one delay device having apredetermined timeconstant.

and responsive to said constant magnitude potential for producing aregulated potential whose amplitude varies as a function of the time ofperistence of said direct current.

4. An electrical computer unit comprising means responsive to a directcurrent for developing an alternating current signal whose phase andamplitude are dependent upon the polarity and magnitude of said directcurrent, means connected with said last-named means for developing aconstant magnitude potential from said alternating current signal, andintegrating means comprising a plurality of delay devices havingdifferent time constants for developing a regulated potential from saidconstant magnitude potential as a function of the time of persistence ofsaid direct current.

5. An electrical computer unit comprising means responsive to a directcurrent for developing an alternating current signal whose phase andamplitude are dependent upon the polarity and magnitude of said directcurrent, means connected with said last-named means for developing aconstant magnitude potential from said alternating current signal, andintegrating means comprising at least one thermal delay device having apredetermined time constant for developing a regulated potential fromsaid constant magnitude potential as a function of the time ofpersistencev of said direct current.

6. An electrical computer unit comprising means responsive to a directcurrent for developing an alternating current signal whose phase andamplitude are dependent upon the polarity and magnitude of said directcurrent, means connected with said last-named means for developing aconstant magnitude potential from said alternating current signal,integrating means for developing a regulated potential from saidconstant magnitude potential as a function of the time of persistence ofsaid direct current, and means for feeding a portion of said regulatedpotential back to said first named means.

7. An electrical computer unit comprising means responsive to a directcurrent for developing an alternating current signal whose phase andamplitude are dependent upon the polarity and magnitude of said directcurrent, means connected with said last-named means for developing aconstant magnitude potential from said alternating current signal, andintegrating means comprising a rst device having a rapid time constant,a second device having a slow time constant and a third device having anintermediate time constant for developing a regulated potential fromsaid constant magnitude potential as a funtcion of the time ofpersistence of said direct current.

8. An electrical computer unit comprising rst means responsive to adirect current for developing an alternating current signal whose phaseand amplitude are dependent upon .the polarity and magnitude of saiddirect current, second means connected with said rst means fordeveloping a constant magnitude potential from said alternating currentsignal, and integrating means connected to the second means andcomprising a thermionic tube having a rapid time constant, a thermal eya'evi having-a slew time aanstaat na-fa Sheena thermal delay devicehavingV a time constant intermediate that'of the tube 4and iirst delaydevice, said thermionic tube and thermal delay devices receiving theVconstant magnitude potential and having their outputs connectedtogether to provide a regulated potential froml said vconstant magnitudepotential as a-"function ofthel time of persistence of'saidVdirectcurrent. l e r 9. An electrical computer unit comprising means'responsive to a direct current kfor developing 'an alternating currentsignal whose phase Vand amplitude are dependent upon the polarity andmagnitude ofsaid direct current signal, means connected 'with saidlast-named means `for developing a constant magnitude potential fromsaid alternating current, and` means for developing'frorn said constantlmagnitude potential a control signal whose amplitude is determined `bythe time of persistence of the direct 'current-signal. v e g '10. Anelectrical computer'funit comprising means re= sponsive to :adirectecurrent for developing an alternating current Whose phase andamplitude are dependent upon the polarity and magnitude of said vdirectcurrent signal, rneans lconnected with said last-named means fordevelopin'gfa constant magnitude potential'from said alternatingcurrentsignal, means for developing from said constant magnitudepotentiala control signal whose amplitude is determined by the time ofpersistence of the direct current signal, and means for modifying saidalternating current signal `by said control'signal. e

will.. An eletcrical computer unit comprising means responsive to Vadirect current signal for developingan alternating current signal whosephase and "amplitude are dependent upon the polarity and magnitudeofsaid direct eurrentjsignaLpmeans connected with said last named meansfor developing a constant magnitude potential'from said alternating'current signal, means for developing fi'ornsaid constant magnitudepotential a control signal Whose amplitude is determined by the time ofpersistence ofr thev direct current signal, means for modifying saidalternating current signal by said control signal and monitor meansresponsive to said control signalandineluding'fsvvitchirg-iiieansopeableinthe event of "e'itee'ss control signal upon Affailure of a portion ofsaid v'cornplut-e'r unittofblockithe eontrol signal.

'-12. -Anfelectrical computer unit comprising means frespoiisivelto adirectcurent'ffor developing an Valternating current signal w'hosepliaseand Y'amplitude are dependent upon vthe polarity and'ma'gnitude of saiddirect current signal, lmeansl connected viithrsaid last named means-Yfor' de velopiriga constant magnitude potential Yfrom saidalternatinfgeurrent signal, integrating means for developing a regulatedpotential from said constant magnitude potentialas "a function yofthetime of persistence of said direct current signal, and monitor meansresponsive to the regulated potential and'including switching meansoperable vintheevent of excess-'regulated potential upon failure of an`velement of Lsaid unit to block theregulated'pot'ential.

13. An electrical computer unit comprising means responsive Ato Aadirectcurrent-'for developing an alternating current signal whose phaseand amplitude is dependent upon the polarity and "magnitude of saiddirect current signal, "means connected with said last named means fordeveloping a constant magnitude potential from said alternating currentsignal, and means for developing from said 'constant' rriagnitudepotential 'a regulated potentialA Wloseamplitude varies'as a function-ofthe time of persistence of said direct'current signal.

R'ern'mces*citen in theme-of this'patem UNITED STATES PATENT OFFICECERTIFICATIGN 0F CORRECTION Patent No 2,969,505 January 24, 1961 Paul ANoxon et, a1

1t is hereby certified that error appears in the above numbered patentrequiring correction and 'that the said Letters Patent should read ascorrected below.

Column 18l line 66, for "funtcion". read function rm; column 19, line21, after "current" insert -1- signal Signed and sealed this 13th day ofJune 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD ttesting Gfficer Commissioner of Patents

